Multi-spot-beam satellite system with broadcast and surge capacity capability

ABSTRACT

A payload design for a multi-spot-beam satellite communication system includes a plurality of uplink spot beam receivers and downlink spot beam transmitters, and a broadcast transmitting subsystem capable of transmitting a broadcast beam to an entire system geographical service area. An input filter-switch-matrix (IFSM) controllably selects input IF signal bands for routing to an on-board digital signal processor-router (DSPR). The DSPR subsequently routes all received point-to-point and broadcast data packets to the appropriate downlink spot or broadcast transmitting subsystems for transmission thereof. The broadcast downlink allows broadcast transmissions to occur at the highest efficiency possible, while also allowing for flexible provision of surge capacity for point-to-point transmissions on previously exhausted spot beams by selective use of the broadcast beam for such point-to-point transmissions.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is a divisional of pending application Ser. No. 09/605,775,filed Jun. 28, 2000 which was a continuation of application Ser. No.08/882,119 filed Jun. 25, 1997, now issued as U.S. Pat. No. 6,175,719 onJan. 16, 2001, the entire contents of both applications beingincorporated herein by this reference.

TECHNICAL FIELD

[0002] The present invention relates to multi-spot-beam satellitecommunication systems, and more particularly to a satellite payloadarranged to provide broadcast and surge-capacity capability tomulti-spot-beam satellite communication systems.

BACKGROUND ART

[0003] Generally, an emerging use of wide-band communication systemsemploying extremely high frequency Ka or V frequency bands is leading todevelopment and implementation of commercial satellite systems whichsupport a large number of high-gain spot beams. Because of high reuse ofthe available frequency spectrum, spot beam technology advantageouslyallows high capacity systems to be realized with a finite number ofbeams. For example, the primary frequency spectrum of the orbit slot istypically divided up equally among several spot beams to form afrequency reuse cluster, e.g., four beams per cluster. Spot beamtechnology also permits reduction of ground terminal size to a pointwhere such terminals become commercially feasible as a mass-marketend-user terminal.

[0004] In known payload designs for multi-beam systems, total capacityof the satellite is generally divided and allocated among the beams on apreferably equal basis so as to accommodate design simplification andcost reductions as well as changes in user demand and market needs. As aresult, such payloads achieve maximum total throughput only when used insupport of point-to-point (PTP) transmissions having an even trafficdistribution among the respective beams at their individual fullcapacities. However, such even distribution is inherently unrealisticbecause certain geographic areas naturally have a higher use demand thanothers. In addition, changing market conditions and other networkingfactors directly impact the distribution of a system's traffic load.Thus, known multi-beam systems operate with a significantly reducedeffective utilization of the satellite capacity when compared to thecapacity with which the beams could otherwise collectively support.

[0005] Another drawback to known multi-beam systems and payload designswhich are inherently suited for PTP transmissions is the loss ofthroughput efficiency when such systems are used to support broadcasttransmissions to be sent to the entire geographic service area.Typically, such systems can only provide broadcast capability if thedesired broadcast information is individually transmitted on every spotbeam in the system.

DISCLOSURE OF THE INVENTION

[0006] Therefore, it is an object of the present invention to provide amulti-spot-beam satellite communication system and method havingimproved utilization of system capacity.

[0007] Another object of the present invention to provide a payloaddesign for a multi-spot-beam satellite communication system which cansupport both point-to-point and broadcast transmissions at an optimumtransmission efficiency.

[0008] Still another object of the present invention to provide apayload design for a multi-spot-beam satellite communication systemwhich can flexibly utilize up to all of a system's broadcast capacity asa surge mechanism to support point-to-point traffic for either uplink ordownlink transmissions for any spot beam whose capacity has beenexhausted.

[0009] In accordance with these and other objects, a first aspect of thepresent invention provides a method of configuring a satellite payloadfor use in a multi-spot-beam communication system including the steps ofproviding a plurality of spot-beam uplinks each of which receive signalstransmitted from a particular section of a total geographic area to beserviced by the communication system, providing a plurality of spot-beamdownlinks each of which transmits signals to a particular section of thetotal service area, and providing a broadcast downlink which transmits asingle wide-area beam to the total service area. Point-to-point servicesare supported by routing point-to-point transmissions received by theplurality of uplinks to a particular one of the plurality of downlinks,while broadcast services are supported by routing broadcasttransmissions received by the plurality of uplinks to the broadcasttransmission link in a non-blocking manner. In addition, the methodfurther can include the step of providing a surge mechanism by routingto the broadcast downlink point-to-point transmissions of any of theplurality of spot-beam uplinks and spot-beam downlinks whosetransmission capacity is exhausted.

[0010] In accordance with another aspect of the present invention, apayload for use with a multi-spot-beam communication system includes aplurality of receiving spot-beam antenna subsystems each arranged toreceive signals transmitted from a particular section of a totalgeographic area to be covered by the communication system, a receivermeans connected to the plurality of receiving spot-beam antennasubsystems for converting each received signal to an intermediatefrequency, and a plurality of transmitting spot-beam antenna subsystemseach arranged to transmit signals to a particular section of the totalservice area. An on-board processor is connected to the receiver meansand the plurality of transmitting spot-beam antenna subsystems forselectively routing received signals to a particular transmittingspot-beam antenna subsystem. A broadcast transmitter subsystem isconnected to the on-board processor and arranged to transmit signals tothe total service area, while an input-filter-switch-matrix is connectedto the receiver means and the onboard processor for selectively routingbands of received signals to the on-board processor in a non-blockingmanner for transmission by the broadcast transmitter subsystem.

[0011] The above objects and other objects, features, and advantages ofthe present invention are readily apparent from the following detaileddescription of the best mode for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 shows the foot-print and layout of a multi-spot-beamsatellite communication system in accordance with the present invention;

[0013]FIG. 2 shows a block diagram of a satellite payload in accordancewith the present invention; and

[0014]FIG. 3 shows a block diagram of a satellite payload in accordancewith a second embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0015] Referring to FIG. 1, a multi-spot-beam satellite communicationsystem 10 is shown having a total service geographic area 12 covered bya relatively large number of uplink and downlink spot beams havingindividual foot-prints 14. High-gain uplink spot beams are preferablyutilized to support small low-power, low cost, end-user earth stationterminals 16, while high-gain downlink spot beams are utilized tosupport high-data-rate transmission to the same small end-user terminals16. More importantly, the combination of uplink and downlink spot beamsprovides for multiple reuse of the same limited frequency spectrum by asingle large satellite 18, thus creating a high-capacity system whichcan serve mass markets for numerous communications services. A networkcontrol center (NCC) 20 provides overall transmission control anduplink/downlink frequency assignment for end users 16 and satellite 18.

[0016] In accordance with the present invention, an area-wide broadcastdownlink beam 22 is integrated into a satellite payload system design100 as shown in FIG. 2. System 100 includes a plurality (i) ofconventional uplink receiver subsystems 102 and a corresponding numberof conventional downlink transmitter amplifier subsystems 104. Thenumber of subsystems 102 and 104 can be any number selected for thesystem based on its design, intended use, cost, and the like. Eachuplink receiver subsystem 102 includes a spot beam antenna 106, anorthogonal mode transducer (OMT) 108 (which separates signals ofopposite polarizations), and a combination of a low noise amplifier(LNA) 110, and a downconverter (D/C) 112. While only one combinationLNA/UC is shown for each uplink receive subsystem 102, a combinationLNA/UC is provided for each of the two signal polarizations received byantenna 102 and 108. For point-to-point (PTP) traffic, each downlinktransmit subsystem 104 includes an upconverter (U/C) 114, an amplifier116, and a spot beam antenna 118. The operation and design of subsystems102 and 104 is well understood in the art.

[0017] An on-board digital signal processor-router (DSPR) 120 preferablyprovides appropriate demodulation, routing/switching, multiplexing, andmodulation of traffic data packets received by satellite 18 intotime-division-multiplexed (TDM) signals. More specifically, all PTPtransmissions (which are sent in the form of data packets) originatingfrom a particular spot or footprint are received by a corresponding oneof the antennas 106 and receiver subsystems 102 and converted to anintermediate frequency (IF) signal. DSPR 120 then processes and groupsthe data packets into individual signals for delivery via an output portto a particular one of the transmitter amplifier subsystems 104 andantennas 118 for subsequent transmission to the designated or addressedspot area.

[0018] In addition to subsystems 104 and corresponding antennas 118,system 100 includes a broadcast downlink antenna 122, an output-filtermultiplexer (OMUX) 130, and a number of broadcast transmitter amplifiersubsystems 124 connected to a plurality of DSPR 120 output ports.Broadcast antenna 122 transmits broadcast beam 22 so that all individualusers in every spot area within service area 12 can receive thebroadcast transmissions. Each broadcast transmitter amplifier subsystem124 includes a set of upconverters (U/C) 126 and amplifiers 128 similarto upconverters 114 and amplifiers 116. OMUX 130 supplies the pluralityof broadcast signals to broadcast antenna 122.

[0019] In further accordance with the present invention, each receiversubsystem 102 is preferably designed to receive the entire primaryfrequency bandwidth of system 10. This contrasts with known spot-beamreceiver subsystems which typically only receive a fixed, individualsub-band. A reconfigurable input filter-switch-matrix (IFSM) 132 isconnected to the plurality of receiver subsystems 102 and the DSPR 120and is controllable via an NCC input 134 and a command decoder 136 toselect any predefined band of each IF frequency spectrum, and connectthe selected bands to appropriate output ports in a non-blockingfashion.

[0020]FIG. 3 discloses a second embodiment 200 of the present inventionwhere like elements to those previously described are denoted with thesame reference numbers. System 200 is arranged to accommodate existingDSPR and satellite designs while at the same time provide broadcasttransmission and surge handling capabilities, and improve systemutilization and efficiency.

[0021] More specifically, system 200 is arranged to operate with asystem frequency plan which allocates the full primary system spectrumof one polarization to uplink-downlink spot-beams for PTP transmissions,while the full primary spectrum of the opposite polarization isallocated for broadcast transmissions utilized with the broadcastdownlink beam. In addition, the broadcast spectrum is assignable inminimum-resolution broadcast (MRB) bands, which are assignable to anyand all uplink spot beams in any combination as configured by NCC 20.

[0022] Further, DSPR input/output ports are assumed to have a fixedamount of bandwidth processing capability equal to 1/K of the primarysystem spectrum on one polarization, where K is the number of MRBsfitting into the primary spectrum. Spot beams on the broadcastpolarization will be received at the satellite by a plurality ofreceiver subsystems 202 having a bandwidth equal to the full primaryspectrum. More specifically, each receiver subsystem 202 is connected toa corresponding OMT 108 in one of the receiver subsystems 102, and to aninput of IFSM 132. Each receiver subsystem 202 includes a set of LNAs204 and downconverters (D/C) 206 similar to LNAs 110 and D/Cs 112.

[0023] IFSM 132 is controlled by ground commands to select a fixedbandwidth equal to the DSPR input port capacity (i.e., 1/K of primaryspectrum) that corresponds to each individual spot beam for PTP traffic,and connects each to a pre-assigned output port for input to a dedicatedinput port of DSPR 120. At the same time, IFSM 132 can be configured byNCC 20 to select any number of MRB frequency bands from each IF signalof each full-band receiver subsystem 202, and deliver each selected MRBband to one of several output ports. As such, the input and output portsof IFSM 132 and DSPR 120 are generally different in their bandwidthhandling capability when used with PTP or broadcast receive/transmitsubsystems.

[0024] With the embodiment shown in FIG. 3, the output broadcast portsof DSPR 120 as a set cannot support more bandwidth than the totalspectrum allocated to the broadcast transmissions in the downlink. Thismeans that the total number of MRB frequency bands selected from all ofthe received full-band IF signals from all spot beams at any instantcannot carry more user data packets than can be correspondingly carriedin the set of broadcast TDM streams. Further, every spot beam can accessthe satellite broadcast section in increments of one MRB up to the fullprimary spectrum, if so configured by NCC 20, and can transmit on all ora portion of a MRB as needed. Thus, depending on the amount of surgecapacity required by each spot, in either the uplink or downlinkdirection, the satellite payload can be configured to deliver thenecessary additional capacity.

[0025] Therefore, the addition and integration of the broadcast downlinkbeam in accordance with the present invention overcomes theaforementioned shortcomings of conventional multi-spot-beam systemdesigns. More specifically, the present invention provides a systemwhich can support all broadcast applications/services at a significantlyhigher transmission efficiency than otherwise possible through the spotbeams. This is achieved because by carrying broadcast services over thebroadcast channels, more of the capacity of each spot beam is availablefor PTP traffic. In addition, the broadcast capacity, accessible to allsystem users in all spot beams, can be selectively used as a surgemechanism to provide additional uplink/downlink capacity to any spotbeam for PTP traffic when the PTP capacity of a particular beam is fullyexhausted. Thus, unpredictable changing market needs and trafficdistribution can be met by assigning capacity to the right mix ofservices and locations throughout the system life cycle. Finally, havingthe surge and broadcast capacity to assign to different beams alsooptimizes the effective utilization of the total satellite capacity. Inother words, use of the surge capacity to continue to keep in service anotherwise exhausted spot beam will inherently increase the utilizationof every other spot beam, and thus that of the whole system.

[0026] While the best mode for carrying out the invention has beendescribed in detail, those familiar with the art to which this inventionrelates will recognize various alternative designs and embodiments forpracticing the invention as defined by the following claims.

What is claimed is:
 1. A method for improving utilization of satellitecapacity of a satellite system that uses multiple uplink and downlinkspot beams, comprising: integrating an area-wide broadcast downlink beamto be used to support point-to-point transmissions of one or more of themultiple spot beams whose transmission capacity has been exhausted.
 2. Amethod as recited in claim 1, further comprising: allocating a fullprimary spectrum of one polarization to uplink and downlink spot beamsfor point-to-point transmissions, and allocating a full primary spectrumof a polarization opposite to the one polarization to the area-widebroadcast downlink beam for broadcast transmissions.
 3. A method asrecited in claim 2, further comprising: assigning the full primaryspectrum for broadcast transmissions in minimum-resolution broadcastbands.
 4. A method as recited in claim 3, wherein the minimum-resolutionbroadcast bands are assigned to any and all uplink spot beams in anycombination as configured by a network control center.
 5. A method asrecited in claim 4, wherein each one of the multiple uplink and downlinkspot beams can access the full primary spectrum for broadcasttransmissions in increments of one minimum-resolution broadcast band andcan transmit on at least